The present invention is related to stainless steel having an improved anti-microbial property, and also related to a method of manufacturing thereof.
Stainless steel represented by SUS 304 has been used as kitchen goods, various devices or tools at hospitals, interior parts for building, grips or poles provided in public transport vehicles, for example, buses or electric trains. However, at the present, time hospital infections caused by Staphylococcus aureus has become a serious problem and it has been demanded that stainless steels for hospital use have the necessary anti-microbial property which eliminates the need for periodic disinfection.
An anti-microbial property can be obtained by forming an organic film or an anti-microbial coating layer, as disclosed in Japanese Patent Application Publication No. 6-10191.
However, such an anti-microbial film or layer has the disadvantage that the anti-microbial function disappears in response to the consumption of the film or layer. In addition, the organic film which loses the anti-microbial function also serves as a nutrition source to promote the undesirable propagation of bacilli or germs.
A complex plating layer containing an anti-microbial component exhibits poor adhesiveness to a substrate, resulting in a coated substrate which is inferior in workability. The external appearance and anti-microbial function become worse due to the dissolution, abrasion and defects in the plating layer.
Further, it is well known that metal elements such as Ag or Cu exhibit an effective anti-microbial function. However, Ag is expensive and unsuitable for a part to be used in a corrosive atmosphere. On the other hand, Cu is relatively inexpensive element and effective as an anti-microbial agent. In this regard, it has been investigated to apply an anti-microbial function to a material such as stainless steel by the addition of Cu.
The inventors have researched and examined the effect of Cu on the improvement of anti-microbial properties, and have determined that the anti-microbial function is enhanced by increasing the concentration of Cu in the surface layer of stainless steel, as disclosed in Japanese Patent Applications Laid-Open 6-209121 and 7-55069 corresponding to Publication Nos. 8-53738 and 8-225895, respectively.